Refrigeration Design Questions

[UNCrefENGR]

Hi everyone, I have just recently come across this site. Currently I’m a college student and left in charge of designing a domestic home refrigerator. Please forgive me if some of the questions I’m about to ask are unclear or information is missing because I’m really new to all this. My question is how do I size my fan (not sure how much cfm I need) and find the overall heat transfer coefficient for a refrigerators condenser. My know values are the temperature changes (hot and cold fluids), refrigerant R-134a, mass flow rate of refrigerant, condenser operating temp. and pressure, how much heat needs to be rejected from the condenser and I would like to use a fin and tube condenser. Hopefully I supplied enough info. and if anyone has some help thanks very much!

[The MG Pony]

Well first it all starts at your opperating temp+ Heat infiltration and RH, forget every thing till you figure that out!

Once you figured that out you size up and select the evap (By this time you'll know the mass flow and such required to get the temp you need) Then you size the compressor that will do that for you.

Then we take total heat from evap + Heat of compression and sum it up to get the condencer * 1.35 = total condencer needed.

Is that what you where looking for?

[UNCrefENGR]

So far I have already determined my evaporator loads and compressor heat, this is the amount my condenser needs to reject (I calculated around 1000 BTU/hr). My question is if I use a fin and tube heat exchanger for the condenser how do I go about finding the needed fan size and overall heat transfer coefficient of the condenser without knowing the outside area of my condenser? There might be something I’m completely overlooking but, basically I’m stuck on how to design a forced convection condenser that will reject around 1000 BTU/hr.

[nh3wizard]

UNCrefENGR are you a basketball fan?:confused: I am disappointed:mad:

[UNCrefENGR]

No I'm not to big on basketball, I attend college at one of the UNC (University of North Carolina) schools.

[nh3wizard]

Good luck to you in your endeavors

[nike123]

Is this what you need?
http://farm3.static.flickr.com/2221/2398642107_d0d04e0927_o_d.jpg

http://farm3.static.flickr.com/2151/2398652461_24654bd74d_o_d.jpg

[Samarjit Sen]

Hi nike,

I very much appreciate your knowledge. I find that you are very handy with the CoolPack. I have the CoolPack, but other than calculating the heat load for Cold room and Air Conditioning I am unable to use it. Could you please guide me as to what all other functions that could be performed. Thank you.

[jahangir.ahmad]

thanks a lot nike
thanks a lot for every thing god will award u for this kindness
jahangir ahmad khan

[The MG Pony]

Did you remember to multiply for the compressor cooling factor? For hermetic it is 35% or so.

[BigJon3475]

http://www.et.web.mek.dtu.dk/Coolpack/Files/Tutorial.pdf

Can you use this?

[nike123]

Hi nike,

I very much appreciate your knowledge. I find that you are very handy with the CoolPack. I have the CoolPack, but other than calculating the heat load for Cold room and Air Conditioning I am unable to use it. Could you please guide me as to what all other functions that could be performed. Thank you.

In Coolpack you have following modules:

Refrigeration Utilities

Refrigeration Utilities is a refrigerant oriented program that can create tables and plots of refrigerant properties. Refrigeration cycle calculations for standard refrigeration cycles can be performed. The program has the following specific features:

Refrigerants:
Log(p),h-diagrams, T,s-diagrams, and h,s-diagrams for 45 refrigerants, including mixtures (R400 and R500 series refrigerants)
Log(p),h-diagrams for 24 of the refrigerants included in RefProp 6.01 (requires the NIST RefProp program, not included in this program).
Calculation of standard refrigeration cycle performance
Tables for thermodynamical propeties for saturated refrigerant (liquid/gas) and for superheated gas
Tables for thermophysical (transport) properties

Moist air:
I,x-diagrams (enthalpy, humidity ratio) for moist air for pressures between 0.014 and 50 bar

Refrigerant calculator

The Refrigerant calculator is a program that can be used to calculate single state point properties for refrigerants. I mostly using him for P-T calculation of refrigerants.

Secondary fluids for heat transfer

Secondary fluids for heat transfer is a program that can be used to calculate transport properties and pressure drop for a range of fluids. I using him for glycol ratio calculation.

Cool cycle analysis

Here program draws Log(p),h-diagram of cycle you analyze. Good diagnostic tool.

CoolTools: Design

ONE-STAGE SYSTEMS:
DX-evaporators

Package of Tools that support the individual phases of designing a refrigeration system.

First level is Cycle analysis (default startup), second level is dimensioning of components, and third level is system simulation with specific components.

Good tool for help in design of DX refrigeration plant.
I use it a lot when I dimensioning simple refrigeration plant for walk-in cold room.

CoolTools: Evaluation

Good for evaluation of changes for energy saving purposes. I didn't used him much here because energy saving is not such issue on small plants, I usually work on, jet.

Compressor calculations

This model can be used to calculate the isentropic and volumetric efficiencies of a compressor from typical catalog data (refrigerating capacity, power consumption, and displacement rate).

The superheat in the compressor inlet is divided into two parts - a useful part originating from the evaporator and an unuseful part caused by heating of the refrigerant in the suction line.

In most of the catalogs, compressor data are stated for testing conditions according to ASHRAE, CECOMAF, ISO and other standards. The data are often presented with a high suction gas superheat and all of this superheat is considered useful (included in the refrigerating capacity). In this model, the testing situation is specified by setting the inlet temperature (T1) to the values specified in the catalog and setting the unuseful superheat to 0 K.

The model can also be used to calculate the compressor performance for other operating conditions (e.g. different values for superheat and subcooling). This part of the calculation assumes that the isentropic and volumetric efficiencies are constant (identical to the know conditions specified). This assumption is only valid if the pressure ratio for the new condition is close the the pressure ratio for the know condition.

Evaporator UA-value

Tool for finding evaporator in catalogs of manufacturers who match your actual working conditions. I use him when selecting evaporators.

Condenser UA-value

Tool for finding condensers in catalogs of manufacturers who match your actual working conditions. I use him when selecting condensers.

Gas pipes - Pressure drop and heat transfer

I using him when dimensioning pipes and insulation thickness's and when troubleshooting pipe related problems.

Liquid pipes - Pressure drop and heat transfer

Same as above


PROPERTIES:
Refrigerants - Thermodynamical and thermophysical (transport) properties
Moist air - Thermodynamical and thermophysical (transport) properties

I didn't used this so far.

COMPARISON OF REFRIGERANTS:
Comparison of three refrigerants in a simple refrigeration cycle

I didn't used this so far.


Cooling demand you already using.
For cold room calculation a recently started to use Calc-Rite load program which is much more handy than Coolpack.

You have tutorial as you see from BigJon post.

If you need any help with software use, feel free to ask. I will try to help as much as I could.

[Samarjit Sen]

Thank you Big Jon and Nike.

I may be bothering nike a number of times in the future for advice and guidance.

[Karol]

What is maximum load, and how is it calcutated (average load is clear). I read coolpack help but still don't understand this.

[kafco]

hi i am new RE.
Will anybody tell me which formula will be used either of these to calculate air required for an air conditioned space area ???.1) -Air flow = volume*no of air changes/60 or 2)Air flow=dehumidified Air flow*dehumudified air rise/Room temp-supply air temp.

[dsltung]

Dear Nike,

Having read your message regarding the CoolPack, I am interested to know more about this software. Can you tell me where can I buy one from? Also what is Calc-Rite load program?

[nike123]

Dear Nike,

Having read your message regarding the CoolPack, I am interested to know more about this software. Can you tell me where can I buy one from? Also what is Calc-Rite load program?

Both of them are free to download and use.
Coolpack download is here (http://www.et.web.mek.dtu.dk/Coolpack/UK/download.html).
Calc-Rite is cooling load calculation software for cold rooms. Download is here (http://www.keepriterefrigeration.com/calcrite/RTcalc2b.htm).

[patrickj]

Dear Nike,
I had being using collpack for sometime but Calc-rite is new to me. Thanks for the link provided
patrickj

[CHAnzardo]

Hello to all the specialists.
I am giving service of change of
coolant of R-22 to R-404A to a unit
RUSSEL, Model: VCD27L22-G
which has a compressing Mark: Copeland
Model: 6DT3-3000-TSK, the unit
one is to a distance of 120 feet of resinto cooled. Please to help me to define the amount of coolant that I must put system so that this it works suitably?
Evaporating Mark: LARKIN, Model: Serial ELT4-1117-4: Heatcraft